1. Field of the Invention
The present invention relates to a toner, a two component developer, a process cartridge and a color image forming apparatus.
2. Description of the Related Art
In image forming apparatuses, such as an electrophotographic apparatus and an electrostatic recording apparatus, a latent electrostatic image formed on a photoconductor is developed with a developer containing a toner so as to form a toner image, and the toner image is transferred onto a recording medium, such as paper, and then fixed by heating, to thereby form an image.
A full-color image is generally formed in such a manner that images are developed with toners of four colors consisting of black, yellow, magenta and cyan, and toner images of respective colors are transferred and superimposed onto a recording medium, and simultaneously fixed thereon by heating, to thereby form the full-color image.
Recently, in terms of energy saving and downsizing of apparatuses, such as an image forming apparatus, it has been demanded to decrease a temperature for heating at the time of toner fixation. A toner having low temperature fixing ability, which satisfies such demand, is desired. Moreover, a toner, which can use at high temperature and high humidity, e.g., a temperature of 45° C. and humidity of 80%, is desired, because image forming apparatuses are used in various environments, and frequencies of air conditioners used are reduced in offices due to promotion of energy saving, or the like.
Generally, the low temperature fixing ability of a toner is improved by a method of decreasing a softening temperature of the toner (News of Sanyo Chemical Industries, Ltd., No. 445, winter, 2007). However, when an image is output using a toner having a decreased softening temperature at high temperature and high humidity, a toner component melted at low temperature is attached to a carrier, causing carrier spent. Consequently, the charging ability of the carrier cannot be maintained, and a normal image cannot be formed.
As a technique of improving the low temperature fixing ability, there is a proposal that a core-shell toner containing a releasing agent, a colorant, a binder resin and a filler is used as a toner for developing an electrostatic charge image. The core-shell toner has ½ outflow temperature measured with a flow tester of 60° C. to 100° C., wherein the shell contains a thermoplastic resin (Japanese Patent Application Laid-Open (JP-A) No. 2006-267231).
However, in the proposed technique, the low temperature fixing ability of the toner is not sufficiently obtained at high temperature and high humidity, and the problem of carrier spent occurring at high temperature and high humidity has not been solved.
Therefore, at present, there is a demand for providing a toner, which has a low temperature fixing ability at high temperature and high humidity, e.g., a temperature of 45° C. and humidity of 80%, and can prevent carrier spent, a two-component developer, a process cartridge, and a color image forming apparatus, using the toner.